What Is Rapid Set Concrete and When Should You Use It?

This article looks at what Rapid Set Concrete is and when it is best to use it for repairs or a quick installation.

What Is Rapid Set Concrete?

Rapid set concrete is a special form of concrete that hardens faster than normal concrete. Often, a modified cement is used or so-called accelerators are added to the cement to increase the speed of the hardening reaction between cement and water. After mixing with water, the reaction between the two components starts immediately. Depending on the type of rapid set concrete, this process can last from a few minutes to an hour.

Remember that setting and curing are two different processes. While setting is the hardening of the concrete to hold its shape, curing is the process the concrete continues to go through over days to develop its full strength. Rapid set concrete shortens the first part of this process, and many rapid set products allow you to work with the concrete within hours as it develops workable strength, while full strength is developed over subsequent days.

Pre-mixed Rapid Set bags are the most common form of this concrete on the market. This is because the raw materials have been accurately measured and made into a product that can be stored on-site until required. It is then a case of following the manufacturer’s instructions on the correct water-to-mix ratio and mixing time for that product.

How Does It Work?

As mentioned previously, when water is added to the concrete mix, the concrete enters the activation phase and starts to form a hard crust almost immediately. There are a few key factors that influence the setting and curing of rapid set concrete, listed below.

• The correct amount of water to mix with the Rapid Set Concrete. Excessive water results in reduced strength and a longer working time.
• Ambient temperature, as setting time is affected by higher and lower temperatures.
• Moisture levels on site
• How well the surface has been prepped beforehand
• Proper finishing once the concrete is placed

Don't be fooled into thinking that just because you’re using a ‘set fast’ product, you can reduce your precast production time by skipping important preliminary work. With adequate surface preparation and correct application techniques, even rapid set concrete needs time to develop.

The Benefits

Faster project completion

Staying productive throughout the day and completing work in time to return to work the following day is important, and Rapid Set helps to achieve this.

Early strength

Early strength allows for loading or early access to the area so you can continue with work.

Better productivity

For busy contractors with multiple projects to complete, the waiting time for concrete to set can prevent them from getting more work done in a day.

Versatility

Rapid set concrete comes in a variety of different formulations, suitable for a wide variety of jobs, including small repairs and fence post construction.

Common Uses

Concrete Repairs

Rapid set concrete can be used for concrete repairs to cracked driveways, damaged footpaths, chipped steps, kerbs and slabs. The area can be put back into use in no time.

Posts, Poles and Fixtures

Fence posts, signposts, mailboxes and other outdoor structures and supports are often set with rapid set concrete. The fence post, for example, is set as soon as possible to prevent slumping prior to consolidating.

Road and Infrastructure Repairs

This type of work is typically performed by councils and contractors undertaking urgent patch repairs on high-traffic roads, trying to keep closures to a minimum.

Landscaping Projects

Small foundations, retaining wall supports and garden structures are typical applications for a product that enables quick progress on a project.

Rapid Set vs Traditional Concrete

• Setting speed: Rapid set is faster, while traditional concrete is slower.
• Early strength: Rapid set develops early strength, while traditional concrete develops strength gradually.
• Working time: Rapid set has a shorter working time, while traditional concrete has a longer working time.
• At work: This type of concrete is best used for repair work and other urgent construction work. Traditional concrete is best used for general construction work.

While Rapid Set is ideal for small and urgent concrete repairs, traditional concrete can still be used, especially for larger amounts of concrete that need to be placed, as it allows for a longer working time to finish off details expertly.

When Should You Use It?

Rapid set is worth reaching for when:

• A repair needs to be finished and usable quickly
• Access to an area needs to be restored sooner rather than later
• You're working to a tight deadline
• Awning columns need to be cast quickly so they can come into use the very next day.
• You need to minimise downtime in commercial or public environments.
• A footpath needs to be re-opened the next day, fence posts are required for a weekend project, or emergency repair work is needed at commercial premises.

When You Might Want to Avoid It

Rapid set concrete doesn't need to be considered for every job. Larger pours need more time to place and finish before setting. Some engineering jobs require a longer set time, and slower cures can be better for some jobs. For most finishing work, a normal mix will give you the time you need.

Common Mistakes to Avoid

• Adding extra water to extend the working time of the product, as this dilutes the mix.
• Skipping proper surface preparation
• Mixing more than you can place before it starts to set
• Ignoring the weather, particularly heat or cold snaps
• Not following the product instructions closely
• Assuming curing care isn’t needed just because setting is quick
• Using a light-duty product for a heavy-load application

Tips for Best Results

• Make sure all tools and materials are ready before mixing begins.
• Measure water carefully rather than guessing
• Mix thoroughly and according to the instructions
• Work quickly and efficiently once mixing begins
• Ensure the surface is clean and prepared prior to the application of Rapid Set Concrete.
• Protect the concrete while it cures
• Choose a product suited to the strength and application you need

Choosing the Right Product

When looking at buying products for concrete, you need to think about the following factors: the type of job you are doing, the speed of set, the strength required, whether the product is for indoor or outdoor use, weather exposure, load bearing, amount required and surface preparation.

Final Thoughts

Rapid set concrete is a great solution when there is limited time, and you still require a reliable solution to complete your work without the wait of a standard concrete mix. Not all jobs are suitable for Rapid set concrete, but for jobs such as repairs, post installs and small landscaping jobs, it can make a huge difference to completing your project in a timely manner. Here at Direct Trades Supply, we carry a range of products to meet the needs of our trade, contractor, DIY and homeowner customers. Our friendly team are happy to assist with any questions regarding the best product for your project and can provide guidance should you require it.